Heretofore, optical isotropic pitch has been prepared from coal pitch or petroleum pitch. Japanese Laid Open Patent Applications 1994-256767 and 1995-18058 teach methods for obtaining superior optical isotropic pitch having excellent stabilization characteristics by particularization of low pressure distillation of and blowing gas into raw materials, such as coal tars. However, the pitch fibers obtained by spinning the optical isotropic pitch obtained from these methods require some protection where high temperatures were applied over long periods in order to stabilize the fibers, and the methods are therefore not entirely satisfactory.
In addition, U.S. Pat. No. 4,789,455 discloses that it is possible to prepare a pitch that may be suitably applied as a high performance carbon material for carbon fibers or other applications by polymerizing conjugated polycyclic hydrocarbons or materials containing them in the presence of an HF/BF, catalyst. When the isotropic pitch thus obtained is used for the manufacture of carbon fibers and the like, melt adhesion of the fibers occurs easily during spinning because of a low softening point, and it takes an extremely long time to stabilize the fibers. Where the softening point of the pitch is raised to decrease the time required to stabilize the fibers, then, as taught by U.S. Pat. No. 4,891,126, the pitch obtained has anisotropic properties and fundamentally has ceased to be an isotropic pitch.
The fact that the time required for stabilization when carbon fibers are prepared from either of the aforementioned coal type or petroleum type pitches is so long is an important problem from the standpoint of produceability. In particular, pitch fibers obtained using optically isotropic pitch as raw material require a long period of time for stabilization compared with pitch fibers obtained using optically anisotropic pitch as the raw material, and the stabilization process is difficult.
With respect to various carbon material applications, such as for use as carbon fibers, activated carbon fibers and anode materials for secondary batteries using a non-aqueous solvent, an optically isotropic pitch that can easily be stabilized as pitch fiber or pitch granules ground to various particle sizes is desired.
Accordingly, it is an object of the present invention to provide a method for making optical isotropic pitch with superior stabilization characteristics for various carbon material applications. It is a further object of the invention to provide a method for producing activated carbon fibers and amorphous type secondary battery material having superior characteristics.